page_title: Submarine communications cable
section_title: Transatlantic telephony
hierarchical_section_title: Submarine communications cable / Early history: telegraph and coaxial cables / Transatlantic telephony
caption_attribution_description: These are submarine telephone/telegraph cables coming ashore at Scad Head on the Isle of en:Hoy, en:Orkney. They terminate in a recent en:British Telecom building but are probably no longer in use. I suspect that they might date from en:World War II as there is a Coastal Gun Battery at Scad Head.
context_page_description: A submarine communications cable is a cable laid on the sea bed between land-based stations to carry telecommunication signals across stretches of ocean and sea. The first submarine communications cables laid beginning in the 1850s carried telegraphy traffic, establishing the first instant telecommunications links between continents, such as the first transatlantic telegraph cable which became operational on 16 August 1858. Subsequent generations of cables carried telephone traffic, then data communications traffic. Modern cables use optical fibre technology to carry digital data, which includes telephone, Internet and private data traffic.
  Modern cables are typically about 25 millimetres in diameter and weigh around 1.4 tonnes per kilometre for the deep-sea sections which comprise the majority of the run, although larger and heavier cables are used for shallow-water sections near shore. Submarine cables first connected all the world's continents when Java was connected to Darwin, Northern Territory, Australia in 1871 in anticipation of the completion of the Australian Overland Telegraph Line in 1872 connecting to Adelaide, South Australia, and thence to the rest of Australia.
context_section_description: While laying a transatlantic telephone cable was seriously considered from the 1920s, the technology required for economically feasible telecommunications was not developed until the 1940s. A first attempt to lay a pupinized telephone cable failed in the early 1930s due to the Great Depression.
  TAT-1 (Transatlantic No. 1) was the first transatlantic telephone cable system. Between 1955 and 1956, cable was laid between Gallanach Bay, near Oban, Scotland and Clarenville, Newfoundland and Labrador. It was inaugurated on September 25, 1956, initially carrying 36 telephone channels.
  In the 1960s, transoceanic cables were coaxial cables that transmitted frequency-multiplexed voiceband signals. A high-voltage direct current on the inner conductor powered repeaters (two-way amplifiers placed at intervals along the cable). The first-generation repeaters remain among the most reliable vacuum tube amplifiers ever designed. Later ones were transistorized. Many of these cables are still usable, but have been abandoned because their capacity is too small to be commercially viable. Some have been used as scientific instruments to measure earthquake waves and other geomagnetic events.
caption: Submarine communication cables crossing the Scottish shore at Scad Head on Hoy, Orkney.
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